Hypergolic propellant systems using tetraformaltrisazine

ABSTRACT

Tetraformaltrisazine is hypergolic with respect to concentrated nitric acid and this fuel oxidizer combination is usable in hybrid combustion systems.

7 a- United States tent 51 3,664,132

Vessel et al. 1 May 23, 1972 54 HYPERGOLIC PROPELLANT SYSTEMS [56] References Cited USING TETRAFORMALTRISAZINE U D STATES PATENTS l' R bert W. Ebelin [72] Imam g f f 3,202,659 8/1965 Wright 149/36 x 3,234,729 2/1966 Altman et a1. ..60/22O g United Aircraft Corporation, East 3,244,702 4/1966 Marcus .I49/36 x ford, Conn.

[22] Filed: Feb 14, 1966 Primary Examiner-Benjamin R. Padgett Attorney-Steven F. Stone [21] Appl.N0.: 527,099

[57] ABSTRACT [52] US. Cl ..60/220, 149/36, 149/74, Tenaformaltrisazine is hypgrgolic with respect [0 concen- 60/219 trated nitric acid and this fuel oxidizer combination is usable [51 Int. Cl. ..C06d 5/10 in hybrid combustion systems. [58] Field oiSearch ..l49/36, 74, 60/219, 228

3 Claims, No Drawings I-IYPERGOLIC PROPELLANT SYSTEMS USING TETRAFORMAL'IRISAZINE This application is related to the copending coassigned US. Pat. application of Eugene D. Vessel, Ser. No. 523,976, filed Feb. 1, 1966, for Hybrid Rocket Fuel Component.

BACKGROUND OF THE INVENTION This invention relates to systems capable of producing hypergolic combustion and more particularly to a system employing a solid fuel material and nitric acid as the oxidizer. As used herein, the term nitric acid refers to the commercially available concentrated nitric acid which is approximately a 68 percent aqueous solution as well as concentrated nitric acid containing dissolved oxides of nitrogen described as red fuming nitric acid (RFNA) and also more highly concentrated nitric acid compositions.

Nitric acid, particularly red fuming nitric acid, is a commercially available, inexpensive oxidizing agent which is commonly used in liquid fuel rocket propulsion systems with such liquid fuels as kerosene, alcohol and hydrazine. The material has quite attractive properties for military applications since it is cheap, storable and is fairly easy to handle in the field.

As a general rule, liquid propellant rocket engines are more complex and susceptible to failure than hybrid propellant engines and it would be desirable, particularly in military applications, to utilize a hybrid propellant engine for missions now using liquid fuels. However, great difficulty has been encountered in developing a hybrid fuel system that is hypergolic with respect to nitric acid, and current systems using nitric acid employ auxiliary ignition systems.

This invention provides a fuel system that is hypergolic with respect to nitric acid and is usable not only in hybrid rocket propulsion systems but also has utility in more general applications such as the generation of heat, light or hot gases.

It is, therefore, an object of this invention to provide a hypergolic combustion system employing a solid fuel and nitric acid as an oxidizer.

It is another object of this invention to employ a solid fuel material containing tetraformaltrisazine, hereinafter referred to as TFTA, in combination with nitric acid to produce hypergolic combustion.

These and other objects of this invention will be readily apparent from the following description.

DESCRIPTION OF THE INVENTION TFTA has the following structural fonnula H2 H2 C C I I HN\ N NH H; H: The material is readily prepared by reaction of formaldehyde and hydrazine as follows:

4CH2O 3N3II4 C4Hi2Nu H (TFTA) The synthesis of TFTA is reported by R. Stole, BER 40, 1505, 1907) and K. Hauifman et al., BER 45, 1728, (I912).

The following example is illustrative of the preparation of TFTA:

EXAMPLE 1 487 grams of a 37 percent solution of formaldehyde in water was added dropwise to 200 grams of a 75 percent solution of hydrazine in water over a period of 4% hours. The reaction mixture was maintained at 50C. Solid TFTA separated upon cooling of the mixture.

According to this invention, TFT A, itself, can be employed as the solid fuel material in which case it is pressed into the desired shape. If necessary, a small amount of a particulate solid binder such as polyethylene or polypropylene can be incorporated to improve the physical characteristics of the pressed grain. TFI'A can also be incorporated in conventional hybrid fuel formulations which may include conventional elastomeric binders such as polybutadiene base polymers, polyether polymers and epoxy polymers, for example; flame temperature modifiers such as powdered metallic aluminum, boron, magnesium and alkali metals, for example; burning rate controllers such as ferric oxide and ferrocene compounds, for example; and solid oxidizers such as ammonium perchlorate and ammonium nitrate, for example.

Since TFTA is a more energetic fuel than the polymeric binders, it is desirable to include as much TFTA as possible in the solid fuel material. Since the hypergolic character of the fuel with respect to nitric acid depends not only on the amount of TFT A present, but also on the nature of the other components in the mixture, and the physical environment in which it is used, it is not possible to set a specific lower limit to the amount of TFTA that is required to produce hypergolic combustion with TFTA. Although experimental results indicate that this lower limit lies in the range between 30-40 percent by weight of TFTA, it is possible that even lower amounts of TF1" A can produce hypergolic combustion with nitric acid in combustion chambers properly designed to reduce heat losses from the fuel. In any event, these lower limits are Well below the level of TFTA that can be readily incorporated in the fuel and therefore no substantial problem exists in incorporating sufficient TFTA in the fuel to produce hypergolic combustion with nitric acid. The following examples are illustrative of this invention:

EXAMPLE 2 Red fuming nitric acid was added dropwise to powdered TFTA. Decomposition followed by ignition and combustion occurred. Further addition of RFNA failed to extinguish the combustion, indicating good resistance to oxidizer flooding.

EXAMPLE 3 Liquid N 0 a more powerful oxidizer than nitric acid was added dropwise to powdered TF1 A. Decomposition and smoke was observed but no ignition occurred even with increased rates of N 0 addition. Apparently, the hypergolic property of TFTA with nitric acid is dependent on some characteristic of nitric acid other than its strength as an oxidizer.

EXAMPLE 4 Solid fuel samples having the following compositions were prepared:

% by wt. by wt. by wt. by wt.

A B C D Hydroxyl terminated polyhutadiene cured with toluene diisocyanate 70 60 50 TFTA 2O 30 40 50 Nitric acid was added dropwise to the samples. Hypergolic combustion occurred with samples C and D, but no combustion was observed with samples A and B.

EXAMPLE 5 A fuel sample was prepared having the following composition:

by weight ERL 2795 epoxy resin 50 Oxiron 200l epoxy modified polybutadiene 12.5 TFTA 37.5

Hypergolic combustion was observed upon dropwise addition of nitric acid.

fuel material in an amount sufficient to produce hypergolic ignition.

2, The process of claim 1 wherein said tetraformaltrisazine comprises at least about 30 percent by weight of said fuel material.

3. The process of claim 1 wherein said nitric acid is red fuming nitric acid. 

2. The process of claim 1 wherein said tetraformaltrisazine comprises at least about 30 percent by weight of said fuel material.
 3. The process of claim 1 wherein said nitric acid is red fuming nitric acid. 